The referenced copending application discloses and claims one approach to the production of electrical energy from high altitude winds. Specifically described therein is a kite-supported module which incorporates airfoil elements in an endless path around a pair of spaced shafts. The contents of that copending application are incorporated herein by reference.
As pointed out in the referenced copending application, many of the wind power projects suggested by the prior art are directed to extracting power from winds at ground level. These approaches have a basic shortcoming due to the relatively low power density and extreme variability in time and location of ground level winds. Typical of these approaches are wind axis "propeller" wind turbines and the cross axis Darrieus "eggbeater" wind turbines in wide use today on California and other wind farms.
The Darrieus unit employs a vertical shaft with two to five curved blades. Another cross axis approach is the "cyclogiro" which employs straight, adjustable pitch, airfoils rotating around a vertical axis. In theory, the cyclogiro wind turbine has the highest predicted power coefficients of all wind turbines (See Mark's Standard Handbook for Mechanical Engineers, eighth edition, pages 9--164 through 9-166).
In addition to the approach contained in the referenced copending application, other proposals have been made for extracting power from high level winds. These approaches are particularly attractive because the energy content of wind goes up as the cube of the wind velocity. One such system is shown in U.S. Pat. No. 3,924,827 of Lois which discloses a series of buoyant wings connected by tethers to an electrical generator. The system is so arranged that, as one wing is being retracted, at least one other wing is being drawn away by the wind to deliver power to the generator.
Another proposal for high altitude wind power extraction is set forth in a paper entitled "Electricity Generation from Jet Stream Wind" by Fletcher and Roberts appearing in the July-August 1979 issue of The Journal of Energy of the AIAA. That paper proposes an airplane-like structure tethered to the ground and carrying wind turbines driving electric generators which deliver electrical current to the ground through two conductors forming part of the tether. The proposal involves flying the device at a relatively high altitude such as 12 kilometers.
The importance of the energy potential of high level winds may be derived from world wind data for 1979-80 available from The National Oceanic and Atmospheric Administration (NOAA). For example, at San Diego in midwinter of 1980, the average wind speed at 40,000 feet was almost 70 miles per hour, as opposed to about 8 miles per hour at sea level, 15 mph at 10,000 feet, 30 mph at 20,000 feet, and 45 mph at 30,000 feet. The available power increases with the cube of the wind velocity but decreases with air density. Set forth in the table below are theoretically available wind power figures in arbitrary relative units for San Diego for midwinter 1980 and midsummer 1979. Wind velocity figures vary widely with time and location, and at many other locations relative available wind power is typically higher at 30,000 feet than 40,000 feet.
______________________________________ Relative Midwinter Rela- Midsummer Altitude Air Wind tive Wind Relative in feet Density Velocity Power Velocity Power ______________________________________ 0 1.0 8 1 8 1 10,000 .74 15 5 6 0.5 20,000 .53 30 28 10 1 30,000 .37 45 66 20 6 40,000 .25 70 167 35 20 ______________________________________
It will be apparent from the foregoing table that winds aloft, especially at high altitudes, have significant potential for energy generation if that potential can be successfully harnessed.
Accordingly, it is a primary object of the present invention to provide improved method and apparatus for harnessing the potential of high altitude winds. Another object is to harness such energy by means of an efficient and relatively simple device which is readily positionable at the location and altitude for favorable wind conditions. Other objects, features, and advantages will be apparent from the following description and appended claims.